Situations arise where a string has to be run between fixed locations in a wellbore such as a seal bore in a liner and a wellhead when running a tieback string between the two locations. In some situations the wellhead load limits require a load sharing arrangement for the weight of the tieback string as between its endpoints. This issue has been solved with an expansion joint that allows the weight below to bear on the liner string while the weight above is supported from the wellhead.
FIG. 1 illustrates a series of progressively smaller strings 10, 12 and 14 that can for example be 22″, 16″ and 14″ respectively. Hanger/packers 18 and 20 respective connect strings 10 and 12 on one hand and 12 and 14 on the other hand. The issue arises as to wellhead weight limits if a tieback string is to be supported on a lower end from string 14. The solution was to use an expansion joint 22 connected to the tieback string 26 with a seal assembly 28 extending into seal bore 24, as shown in FIG. 2. Weight is transferred at ring 30 to the liner 14 but the use of the expansion joint 22 allows the weight of the tieback string 26 above it to be carried by a wellhead that is not shown.
As noted before, the expansion joint 22 allows for proper space out at the wellhead as the joint 22 has a predetermined stroke and can be compressed for installation for support at the wellhead. Once installed and put into production or injection service there are changes in stress experienced by the tieback string principally due to thermal effects. In the past the stress issue has been addressed in several ways. One way is to allow the expansion joint the ability to elongate or shrink depending on the nature of the loading. Another feature is to provide a release feature that combines locking with movement in opposed directions but employs a collet system so the that the collet fully releases to unlock the expansion joint when a predetermined stress is reached to avoid stress failure at another location on the tieback string such as at the wellhead.
The problem with such designs as illustrated in U.S. Pat. No. 4,778,008 is that in the locked position of FIG. 1 with a gap between surfaces 34a and 24a there can be movement in opposed directions of the joint 1 that will over time wear out the stacked chevron seals 21 all without triggering a release from overstress which will result in collet 24 jumping past the stop 34.
The present invention seeks to preserve the beneficial purpose of an expansion joint for initial spacing out by providing for relative movement in a single direction so that the upper end can be accurately positioned for connection to a wellhead. The joint can thereafter shrink in length due to thermal or other loading but it is locked against getting longer. What this does is eliminate the cycling of the expansion joint that tends to wear out its seals prematurely.
Locking devices such as body lock rings have long been used to hold the set in downhole packers in a variety of designs and in a variety of applications. Some examples are U.S. Pat. Nos.: 4,582,265; 4,754,812; 4,479,544; 7,080,693; 8,109,339; 5,197,546; and 7,677,303.
Those skilled in the art will better appreciate additional aspects of the present invention which minimizes seal wear with a one way locking feature that permits the joint to compress but prevents extension of the joint by a review of the detailed description of the preferred embodiment and the associated drawings while recognizing that the full scope of the invention is to be found in the appended claims.